Group-of-curves pattern identification apparatus

ABSTRACT

A pattern of a group of curves, such as fingerprints, including noises or discontinuities is formed from a permanent magnet film magnetiized in a direction perpendicular to its surface. Disposed on the permanent magnet pattern is a single crystal plate having an easy magnetization axis only in the same direction as the perpendicular direction of the permanent magnet pattern. A bias magnetic field is controllably applied in a direction perpendicular to the surface of the single crystal thin plate-let to form a figure of magnetic domains in the single crystal thin plate-let in a manner to correspond to the permanent magnet pattern. According to a group-of-curves pattern identification apparatus of this invention the magnetic domains are represented in the form of noise or discontinuity-free optical image.

United Stat Outeru et a1.

[4 1 Apr. 16, 1974 Assistant Examiner-V. P. McGraw [57] ABSTRACT A pattern of a group of curves, such as fingerprints, including noises or discontinuities is formed from a permanent magnet film magnetiized in a direction perpendicular to its surface. Disposed on the permanent magnet pattern is a single crystal plate having an easy magnetization axis only in the same direction as the perpendicular direction of the permanent magnet pattern. A bias magnetic field is controllably applied in a direction perpendicular to the surface of the single crystal thin plate-let to form a figure of magnetic domains in the single crystal thin plate-let in a manner to correspond to the permanent magnet pattern. According to a group-of-curves pattern identification apparatus of this invention the magnetic domains are repre sented in the form of noiseor discontinuity-free optical image.

4 Claims, 11 Drawing Figures PATEMEDAPR 16 1914 SHEET 1 OF 3 FWG.4

FWG.4B

FIG.3

PATENTEU kPR 16 I974 SHEU 2 [IF 3 GROUP-OF-CURVES PATTERN IDENTIFICATION APPARATUS This invention relates to a group-of-curves pattern identification apparatus capable of eliminating noises or discontinuities as found in a pattern of a group of curves such as a fingerprint.

Up to this time, notwithstanding a great necessity, the automatic identification or classification of fingerprints is considered as very troublesome because of many noises or discontinuities contained in the pattern, and there are no simple practical devices for the automatic identification or classification of fingerprints. To make clear the importance of this invention, at first it is explained how this noise elimination is troublesome and difficult. A fingerprint has many discontinuuities of ridges as shown in FIG. 1, and the pattern of discontinuities presents a variety of figures or outward appearances as the case may be. To check the identity between a fingerprint and a reference one, it is required to extract the features of them correctly without being puzzled by the noises, and the modification of the pattern must be made as shown in FIG. 2 by checking whether a discontinued portion is a noise or not. For the observer, it is comparatively easy to make such modification by a hand while observing with eyes. However, it is very troublesome practically to perform this modification in every case and an automatic groupof-curves pattern identification apparatus is strongly demanded. However, the realization of this apparatus is more difficult than one may think, as will be explained below. i

For example, a portion shown by a point P in FIG. 3 is on a ridge if there is no noise. However, the portion may be regarded to be out of a ridge if only the neighbourhood of this portion is observed locally as shown by a full line circle in FIG. 3. If the area under observation is widened as shown by a dotted line circle, neighbouring black portions appear. In this case, however, it is impossible to recognize whetherthese black portions are parts of the same ridge as shown in FIG. 4A or not as shown in FIG. 4B. The recognition is made by widening the observed area more widely and finding out the direction of the neighbouring ridge. The observers are able to easily recognize whether the portion is a part of a ridge or not, since he can observe a wide area in a moment and find out'the direction of the flow line of every ridge. The realization of the observers function by a machine is so difficult as explained below. For example, if a small spot is illuminated by a small spot light which is oscillating within a range of fl from the point P as shown in FIG. 5, the intensity of the penetrating light integrated with respect to time depends on the quantity of the black portion. For the change of the oscillating direction, the intensity of the penetrating light changes. If the portion P is part of a ridge as shown in FIG. 4A, the intensity of the light for the change of the vibrating direction is steeply varied. On the other hand, if the portion is not part of a ridge, the change is not steep. As the derivative of the intensity change of the penetrating light is detected and compared to a reference value, it is considered possible to realize a groupof-curves pattern identification apparatus for fingerprints. However, still more difficulty will appear, because there are encountered various cases in real fingerprints which one can not think of. Considering the fact that such a portion as the point P represents only a very small area of the whole pattern and such a process as stated above must be repeated over the whole pattern, one can easily imagine how troublesome and difficult the noise elimination is.

Accordingly an object of this invention is to provide a group-of-curves pattern identification apparatus capable of eliminating noises or discontinuities as found in a pattern of a group of curves such as fingerprints.

The above object is attained in accordance with the present invention by providing a group-of-curve pattern identification apparatus including a transparent substrate having flat surfaces; means formed from a permanent magnet film in a manner to correspond to a group of curves to be recognized, and disposed on the surface of the substrate; a magnetic thin plate-let bonded to the group-o'f-curves means and having an uniaxial anisotropy oriented in a direction normal to the surface of the substrate; means for controllably applying a bias magnetic field in a direction perpendicular to the composite plate assembly; and means for detecting the figure of magnetic domains in the magnetic thin plate-let.

According to the present invention there is provided an ingenious group-of-curves pattern identification apparatus capable of easily eliminating noises or discontinuities which present difficulty in recognizing a pattern of a group of curves such as fingerprints.

The present invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 is a view showing a fingerprint pattern of a group-of-curves including noises or discontinuities;

FIG. 2 is a view showing a fingerprint pattern obtained by eliminating the noises or discontinuities;

FIG. 3 is a partially enlarged view of FIG. 1;

FIGS. 4A and 4B are views explaining whether or not any point P of the noises or discontinuities 40 falls on a flow line of each ridge of the fingerprint pattern;

FIG. 5 shows a principle explaining whether or not the point P in FIG. 3 is on a flow line of the ridge of the fingerprint;

FIG. 6 shows the construction of a group-of-curves 7 pattern identification apparatus according to this invention;

FIGS. 7A to 7C show the distribution of magnetic domains in a magnetic thin plate-let having a uniaxial'anisotropy oriented in a direction normal to its platesurface; and

FIG. 8 shows a flow line of the fingerprint pattern obtained according to this invention.

There will now be explained one embodiment of this invention by reference to the accompanying drawings.

As shown in FIG. 6, numeral 1 is a flat transparent substrate such as a glass plate. Disposed on the substrate is a fingerprint pattern 2 formed from a thin permanent magnet film magnetized in a direction perpend icular to its surface. 3 is a thin plate-let era sihglecrystal of orthoferrite or iron-garnet having an easy magne'tization axis only in a direction perpendicular to the plate surface. On both sides of this composite plate are disposed coils 4 for applying a magnetic field in a direction perpendicular to the plate. The coils 4 are serially connected, through a variable resistor 5 and a switch 6 for polarity change, to a DC current source 7. A light source 8 is located under the composite plate, and the light beam from the light source 8 is linearly polarized through a polarizer 9, and is projected onto the composite plate. The light passing through the composite plate is led to the observer's eyes or a camera 12 through an analyzer 10, within a microscope 11, whose polarization axis is displaced 90 from that of the polarizer 9. Therefore, if there is nothing to change the polarization angle between the polarizer 9 and the analyzer 10, the field of vision is entirely dark.

In order to make clear the principle of this invention, it is necessary to explain the characteristics of a single crystal thin plate -le t of orthoferrite or iron-garnet. The single crystal plate-let has a strong uniaxial anisotropy along a special direction, c axis in orthoferrite for example, and is magnetized only along this axis. If the single crystal is cut normal to the axis into a plate-let, the plate-let is magnetized only along its normal. If no magnetic field is applied to the plate-let, the distribution of magnetic domains in the plate-let becomes striped as shown in FIG. 7A. As shown in FIG. 78, when a bias magnetic field is applied along the normal of the platelstsarfsse lhsstriavmattasa nts black i F G- 7B are narrowed in width or cut, and vanished eventually under a strong bias field as shown in FIG. 7C, i.e., the plate-let is entirely magnetized or saturated in one direction. After saturation, the same magnetic state is held even without application of the bias field. However, when a reverse bias field is applied to this plate, magnetization reversal of the magnetic domain appears dependent upon the strength of the reverse bias field. If there is a variation of the bias field strength, the stripe domains with the same direction of magnetization as that of the bias field move toward the portion where the bias field is stronger. A coercive force He for this wall movement of the stripe domains is smaller than 0.5 oe. Therefore, if the permanent magnet pattern is contacted with the single crystal plate-let as shown in FIG. 6, the stripe domains magnetized in the same direction as that of permanent magnet pattern is attracted to the permanent magnet pattern. As the magnetic domain wall has an energy called domain wall energy," the area of the magnetic domain wall has the tendency for the domain wall length to be contracted. This is analogous to the surface tension of a liquid drop or a soap bubble. Therefore, a stripe domain withstands a local expansion or a local depression from a normal stripe form. Let us assume that the magnetization of the permanent magnet 2 is directed upwards in FIG. 6. At first, when the bias coils 4 are excited so as to produce a bias magnetic field upwards, then the almost whole area of the single crystal plate-let is magnetized in the direction of the bias field. After the increase of resistance of the resistor the polarity of the bias field is reversed by the switch 6, and the strength of the bias field is gradually increased until the magnetic domains with same magnetization direction as that of the bias field covers the whole area of the platelet except the portions over the permanent magnet pattern, to which the stripe domains with an opposite polarity to the bias field are attracted. Though the permanent magnet fingerprint pattern has many thin portions and discontinuities as shown in FIG. 3, the stripe domains under the permanent magnet pattern are not cut by these noises (thin portions and discontinuities) because of the surface tension of the domain wall. Thus, the group of the stripe domains over the permanent magnet pattern presents a complete fingerprint pattern with no discontinuities or noises.

The shape of the stripe domains can be easily represented by a combination of the polarizer 9, analyzer 10, camera 12 and microscope ll utilizing the Faraday effect (or Kerr effect) as will be explained below. As the black portions and white portions in FIG. 8 have an up ward magnetization and downward magnetization, respectively, to a paper surface, the polarization angle of a penetrating light is rotated by +6 and -8 according to the direction of magnetization. When the angle of the analyzer is shifted by +8, the portion with the up ward magnetization becomes dark, and the portion with the downward magnetization becomes bright. Therefore, a picture taken by the camera 12 in FIG. 6 shows no noise (or discontinuity). As explained above, the noises in a complex curve such as a fingerprint pattern can be easily eliminated according to this invention. In view of the difficulty as conventionally encountered in eliminating such noises in the intricate curve, it will be appreciated that this invention constitutes a significant departure from the state of the art.

What we claim is:

1. A group-of-curves pattern identification apparatus comprising a transparent substrate; means formed from a permanent magnet film in a manner to correspond to a pattern of a group of curves, and disposed on the substrate; a magnetic thin plate-let bonded to the group-ofcurves means and having a uniaxial anisotropy oriented in a direction normal to the surface thereof; means for applying a bias magnetic field in a direction perpendicular to the composite plate assembly of said transparent substrate, said group-of-curves means and said magnetic thin plate-let; means for controlling a magnetic field from said bias magnetic field applying means; and means for detecting a figure of magnetic domains in the magnetic thin plate-let.

2. A group-of-curves pattern identification apparatus according to claim 1 in which s agl magneticfield applying means comprises coil means disposed on both sides of said composite plate assembly; and a DC power source for passing electric current through the coil means.

3. A group-of-curves pattern identification apparatus according to claim 1 in which said control means consists of switching means for polarity change incorporated within said bias magnetic field applying means and a variable resistor.

4. A group-of-curves pattern identification apparatus according to claim 1 in which said magnetic domain figure detecting means comprises a light source and a polarizer both disposed on one surface of said composite plate assembly; an analyzer, within a microscope, disposed on the other side of said composite plate assembly; and a camera device coupled to the microscope. 

1. A group-of-curves pattern identification apparatus comprising a transparent substrate; means formed from a permanent magnet film in a manner to correspond to a pattern of a group of curves, and disposed on the substrate; a magnetic thin plate-let bonded to the group-of-curves means and having a uniaxial anisotropy oriented in a direction normal to the surface thereof; means for applying a bias magnetic field in a direction perpendicular to the composite plate assembly of said transparent substrate, said group-of-curves means and said magnetic thin plate-let; means for controlling a magnetic field from said bias magnetic field applying means; and means for detecting a figure of magnetic domains in the magnetic thin plate-let.
 2. A group-of-curves pattern identification apparatus according to claim 1 in which said bias magnetic field applying means consists of coil means disposed on both sides of said composite plate assembly; and a DC power source for passing electric current through the coil means.
 3. A group-of-curves pattern identification apparatus according to claim 1 in which said control means consists of switching means for polarity change incorporated within said bias magnetic field applying means and a variable resistor.
 4. A group-of-curves pattern identification apparatus according to claim 1 in which said magnetic domain figure detecting means consists of a light source and a polarizer both disposed on one surface of said composite plate assembly; an analyzer, within a microscope, disposed on the other side of said composite plate assembly; and a camera device coupled to the microscope. 